nutritional biochemistry

Question 1

digestive (gastrointenstinal) system

Answer 1

alimentary canal/ GI tract- organ that food passes through (mouth –> anus)
peristalsis begins in throat- muscular contractions
accessory organs- foods do not pass throughthem but they help to make the digestive systems function properly
salivary glands- produce saliva which moistens food to help it move through dig system
bile- involved in breakdwon of dats
gallbladder- hekps to release bile to small intestine

Question 2

GI tract

Answer 2

mouth
oesophagus
stomach
small inestine
large intestine
anus

Question 3

accessory organs

Answer 3

salivary glands
liver
pancreas
gall bladder

Question 4

process

Answer 4

1. digestion- process by which foods are broken down into molecules- mechanical (breaks up food into smaller pieces) and chemical (broken down by chemical agents- enzymes, acid and bile)
2. absorption- process of taking products of digestion (molecules) across GI tract walls into circulation
3. elimination- process by which undigested food and waste products are removed from body

Question 5

cephalic phase

Answer 5

stage of digestion that starts before you eat
anticipatory phase- physiological response to sensing/ expecting food
prepares gi tract for food processing
vagus nerve increases signal the production of saliva, bile, stomach acid, enzymes, gastric acid + pancreatic horomones, promots gut motility (para Ns)

Question 6

chemical digestion

Answer 6

major components of diet- starches, sugars, fats + proteins must be hydrolysed into their smaller constiitent molecules for absorption and metabolism to occur
enzymatic hydorlysis can break the bonds holding the molecular building blocks within the food together

Question 7

peristalis

Answer 7

takes place in oesophagus, stomach and S/LI
propels food down the GI tract using wave like muscle contractions
occurs in longer muscles
helps water absorption in LI

Question 8

segmentation

Answer 8

mixes chyme into contact with intestianl wall to help movement through digestive system
occurs in circular muscle
only occurs in SI

Question 9

stomach

Answer 9

lies between oesophagus and duodenum
plyoric area- where grinding of solid food takes place
plyoric sphincter- controls entry or food from stomach into small intesntine
peristalic movemnt helps to move food down and push it towards duodenum and SI

Question 10

small intestine

Answer 10

longest part of the digestive tract- main site of digestion and absorption of food
villi increase the SA of the intestine where absorption is carried out
microvilli are hair like structures which further increase the SA of each cell- maximising absorption potential

Question 11

carbohydrate digestion

Answer 11

starch broken fown by salivary amylase into individual glucose molecules
occurs in mouth- amylase- breaks down into maltose and smaller polysaccharised + small intestine
low pH of stomach inhibits salivary amylase to starch
pancreatic amylase- continues breakdwon of starch into shorter strands of glucose in small intestine
disaccharides bare broken down into simple sugars in small intestine

Question 12

carbohydrate absorption

Answer 12

absorption of glucose, galactose and fructose in internal enterocyte
fructose absorbed by GLUT 5- membrane transporter, into enterocyte
glucose and galactose absorbed by SGLT1 (sodium glucose co transporter) into enterocyte
from enterocyte into capillary by GLUT2 transporter (all 3)

Question 13

glucose in liver

Answer 13

fructose and galactose mainly converted into glucose
glucose stored as liver glycogen (glycogenesis)
glucose that is not stored is used to produce energy (glycolysis)
stored as muscle glycogen
converted/ stored as fat

Question 14

protein

Answer 14

large molecule made up amino acids
essential amino acids cannot be synthesises by the body in sufficeient amounts- must be obstained in diet
non-essential amino acids can be synthesised by the body

Question 15

protein digestion

Answer 15

occurs in stomach and small proteins
whole proteins are chewed and swallowed into the stomach
gastric juices containing HCL released- HCL: denatures proteins, unfolding their 3d structure to reveal polypeptide chain
enzymatic digetsion by pepsin forms shorter polypeptides
small inestine
- pancreas secretes digestive juices which further breakdown polypeptides (trypsin and chymrotrypsin)
- break down proteins into tri and dipeptides - amino acids can move across SI and are broken down further in enterocytes + can be absorbed into bloodstream

Question 16

amino acid absorption

Answer 16

taken up by liver cells
used for protein synthesis in cells around the body
converted to glucose by gluconeogenesis
used for cellular respiration
rearranged and stored as fat - no storage form of protein

Question 17

fats

Answer 17

main type of lipid in food are triglycerides
made up of glycerol unit and 3 FA chains
structure determines their impact on health and melting point
depedndent on their dominant chemical structure- saturated (no c bond), monounsaturated (1 carbon bond), polyunsaturated (>1 carbon bond)

Question 18

fatty acid classification

Answer 18

most FA contain 4- 24 carbons with even no. of carbon occuring more freq than odd
FAs are classified based on carbon chain length
short chain= <6
medium chain= 6-10
long chain = >12

Question 19

fat

fat breakdown

Answer 19

in stomach, lipase activity helps to start breaking trigkycerides down into diglycerides and fatty acids
emulisfication of lipids in the SI- lipids are brojen down into smaller emulsified fat droplets, bile salts break down the larger fat globule into emulsified fat droplets, increased SA for enzyme action to attach and break down triglycerides further

Question 20

fat absorption

Answer 20

micelles help fats get close enough to microvilli of intestinal cells so that they can be absorbed
fatty acids and monoglycerides from fat digestion leave micelles and enter intestinal epithelial cells- diffuse across membrane into enterocytes
into bloodstream
- short and medium FA can be absorbed directly into bloodstream
- long chain FA and monoglycerides reassemble into triglycerides within intestinal walls + are incorporated into chylomicrons

Question 21

absorbed lipids

Answer 21

liver is involved in fat metabolism and synthesised lipoportiens, chloesterol and phopsholipids essential for many body functions
metabolic fate of lipid depends on dietary intake levels and energy expenditure
if fat intake is in excess- liver will prepare for storage in subcutaneous tissue via lipogenesis
if energy and glucose levels are low, stored fat is converted back into glycerol and fatty acids via lipolysis

Question 22

gastric emptying

Answer 22

process by which the contents of the stomach are moved into the duodenum
appropriate passage of nutrients and indigestavle particles through the GI tract is only possible with a regulated progress
allows for absorption of digested food into the blood
determined by the coordinated motor activity of the stomach and proximal intestine- involves smooth muscle, neural and hormonal factors

Question 23

hormonal control of GE

Answer 23

ghrelin- stomach- accelerate gasrtic emptying, stimulate appetite
gastric inhibitory polypeptide (GIP)- intestinal K cells
glucagon like peptide 1 (GLP1)- intestinal L cells
peptide tyrosine tyrosine (PYY)- intestianl L cells
all delay gastric emtying and reduce appetiete

Question 24

solid and liquid gastric emptying

Answer 24

2 phase GE of solid meals
1. intitial delay (lag period <30 mins) before emptying begins
2. linear pattern of emptying
liquid meals generally empty the stomach in exponential manner
GE rates vary with the physical characteristics and energy density of food

Question 25

factors that slow GE

Answer 25

solid vs liquids
fat vs carb and protein
increased energy density
acidity
larger volume and particle size

Question 26

importance of GE on exercise

Answer 26

GI tract plays a critical role in delivering carb and fluid during prolonged exercise
GI function is not alwasy optimal in endurance conditions
energy delivery from the stomach to the SI can be altered by exposure to specific nutrients/previous dietary histiry

Question 27

study- gastric emptying

Answer 27

can be altered by short term increased exposure to specific nutrients
dietary supplemtation with 400g per day of glucose for 3 dats sig increased GE vs the standard diet alone
rapud and specific adaptation of SI regulatory mechanisms for GE of nutrient solutions can occur in response to increases in dietary load

Question 28

gut training

Answer 28

may reduce exercise associated GI symptoms- partly due to GR adaptation/reduction in sensitivity to nutrient expoure- could lead to potential exercise performance benefites

Question 29

importance of GE

Answer 29

slower rate of GE leads to lower postpradial (fed state) rise in macronutrient and consequently a lower postprandial burden on the clearance of these macronutrients from the circulation
postprandial triglyverol (TG) concentrations- impaired clearence= independent CVD risk factor
small differences in GE can have major impact on postprandial glycaemia in health and T2D
GE is linked to satiety, appetiite and hunger aswell as chronic food intake and energy homeostasis

Question 30

gastroparesis

Answer 30

delayed GE- slowed gastric movement + food is stopped within the stomach

diabetes is most common known cause of gastroperosis, can damage vagus nerve cells and cells in the wall of the stomach

Question 31

measurement of GE

Answer 31

measuring GE aids diagnosis and treatment of GI related disorders such as gastroparesis, T2D and dyspepsia related disorders incl crohns and inflammatory bowel disease
can help nutrition studies to further understand the metabolic response to food
acrruate measure of GE is important as small differences can have a major impact on postprandial glycemia in health and T2D
measurements of GE help us to understand rise in macronutrients and a lower postprandial budern on the clearence of these MN from circulation

Question 32

GE scintigraphy

Answer 32

gold standard for quantifying GE time
1. radiolabelled egg based meal consumed
2. serial measurement of radioactivity in stomach
directly correlates with the volume of meal remaining in stomach at certain time

best validated method
expensive, exposes patients to radiation

Question 33

13C- octanoic acid breath test

Answer 33

in stomach, 13C octatonic acid (medium chain FA) is firmly retained in the yolk of egg used as test meal
once the meal reaches the duodenal lumen- 13C octanic acid is rapidly absorbed through the intestinal mucosa and oxidised to 13co2 in liver

non invasive + non radioactive, inexpensive
indirect estimation of GE

Question 34

wireless pH and motility capsules

Answer 34

patients ingest a non-digestibly wireless motility capsule after a standardised meal
capsule measures pressure, pH and temp as it travels down the GI tract
GE can be measured based on time from ingestion until a sharp rise

non radioactive, east of conduct,
no info on dynamics of GE in different periods (only emptying), not widely used